Accelerometers, which are responsive to linear acceleration, are disclosed in U.S. Pat. Nos. 7,047,808 and 7,267,006. The described accelerometers are of the variable capacitance type, comprising a proof mass movable between fixed capacitor plates. They are constructed in silicon as MEMS devices, with a proof mass on a thin suspension so as to be movable, which is sandwiched between two fixed capacitor plates each at a small gap from the proof mass. Under the effect of acceleration on the accelerometer one gap increases and the other decreases to give a differential output signal. The construction includes interdigitated fingers, which increase sensitivity and increase gain to get the noise down. This construction is shown in FIG. 1, which includes a plate-like proof mass 1, four flexible mounting legs 2 co-planar with the proof mass 1, which are mounted between the mass 1 and a ring-like support 3. The proof mass 1 is mounted for linear movement in its plane and in a sensing direction 4, in response to acceleration applied to the accelerometer. Interdigitated fingers 9 comprise fixed first, second, third and fourth arrays 5, 6, 7, 8, which interdigitate with respective arrays 10, 11, 12, 13 extending from proof mass 1. Gaps between fingers are made as small as possible, in order to increase sensitivity and provide the lowest noise possible. An output signal is taken from the proof mass, and applied to a charge amplifier. Problems which arise are firstly that only a restricted range of g values may be measured, due to saturation of the charge amplifier. Secondly, there is a problem of non-linearity in measurements, being caused by temperature variation, and also by the mechanical construction of the accelerometer, mainly the ratio of the proof mass displacement to the interdigitation gap. Such non-linearities introduce uncertainties into the measurement of acceleration.
U.S. Pat. No. 6,651,499 discloses a gyroscope, which is responsive to variable rates of rotation, and which is constructed as a planar ring vibrating structure. The gyroscope is coupled to a closed loop control system, which maintains control over primary drive and secondary drive, and maintains a pick off at a null value. The minimum detectable rotation rate that can be resolved is determined by electronic noise in a pick off amplifier. In order to maintain sensitivity whilst having the capability of measuring a wide range of rotation rates, a scale factor variation is introduced within closed control loops. This is effective to dynamically scale the output signal in proportion to the reducing amplitude of motion as the input angular rate increases thereby giving a broader input rate range.